290 A MANUAL OF PHYSIOLOGY 



wave is started it travels up the intestine only for a short 

 distance and then dies out. The movements of the large 

 intestine do not differ essentially from those of the small. 

 They start at the ileo-caecal valve and travel downwards, but 

 do not normally reach the rectum, which, except during 

 defsecation, remains at rest. 



Influence of the Central Nervous System on the Gastro-in- 

 testinal Movements. As we have already said, these move- 

 ments are much less closely dependent on the central nervous- 

 system than are those of the oesophagus ; they can not only 

 go on, but are in general better marked when the extrinsic 

 nervous connections are cut ; they cannot spread when the 

 continuity of the tube is destroyed, and the mere presence of 

 food will excite them when other than local reflex action has 

 been excluded by section of the nerves. Nevertheless, the 

 central nervous system does exercise some influence in the way 

 of regulation and control, if not in the way of direct initiation 

 of the movements, and the swallowing or even the smell of 

 food has been observed to strengthen the contractions of a 

 loop of intestine severed from the rest, but with its nerves 

 still intact. The vagus is the efferent channel of this reflex 

 action : stimulation of its peripheral end may cause move- 

 ments of all parts of the alimentary canal from oesophagus 

 to large intestine, except the cardiac end of the stomach 

 (Meltzer), and may strengthen movements already going on ;. 

 but section of it does not stop them, nor hinder the food 

 from causing peristalsis wherever it comes. The vagus also 

 contains inhibitory fibres for the lower end of the oesophagus 

 and the whole of the stomach, including the cardiac sphincter. 

 The splanchnic nerves contain fibres by which the intestinal 

 movements can be inhibited, and they appear to be always 

 in action, for after section of these nerves the movements 

 are strengthened. On the other hand, stimulation of the 

 peripheral end of the cut splanchnic causes arrest of the 

 movements. Occasionally, however, it has the opposite 

 effect. Contractions of the small intestine are more easily 

 caused by excitation of the vagus after the inhibitory 

 splanchnic nerves have been cut. 



The lower part of the large intestine is influenced by the sacral 

 nerves (second, third and fourth sacral in the rabbit), and by certain. 



